The present invention relates to a reception path search method and searcher circuit for use in such method of a CDMA (Code Division Multiple Access) reception device.
The CDMA communication system enables communication with high quality to be implemented under very low Eb/No (signal power in every 1 bit/noise power in every 1 Hz). The CDMA communication system is used in conjunction with diversity technique using multi-path propagation (RAKE), the technique of large error-correcting code of coding gain, transmission power control technique and so forth. The CDMA communication system in conjunction with the above techniques brings such high quality communication. In recent years, the CDMA communication is applied extensively in mobile communication and so forth.
On the other hand, in the CDMA communication system, the reception signal is diffused using diffusion code. The diffused reception signal is subjected to inverse-diffusion by a diffusion code in the reception side. At the time of the inverse-diffusion of the diffused reception signal, 20 chip timing (reception timing) of the diffusion code should be accurately synchronized with the reception signal diffused by using the diffusion code indispensably. Particularly, in the case of mobile communication, there exist a great many reception paths which are changed from moment to moment. In such the case, the most appropriate reception path should be selected regularly. Reception timing of respective reception paths is necessary to be synchronized with reception signal to be followed correctly.
For instance, the Japanese Patent Application Laid-Open No. HEI 9-181704 (hereinafter referred to as a first prior art) discloses xe2x80x98MULTIPATH SEARCH METHODxe2x80x99. In the multipath search method, the CDMA reception device is provided with a set of search-finger and plural sets of tracking-fingers. The search-finger detects intensity level of reception signal concerning reception timing corresponding to delay range of the reception path supposed previously. The search-finger selects the most suitable plural reception paths to allocate plural reception paths to respective tracking-fingers. The tracking-finger tracks the respective reception paths in detail.
FIG. 1 is a conception view showing basic operation of the above first prior art. Its (a) indicates a reception signal. The search-finger executes correlating detection with reception signal using diffusion code in which chip timing is changed gradually with information N symbol as search range. A delay profile with reception timing shown in (b) as the horizontal axis, and with intensity level of reception signal as the vertical axis is obtained. The intensity level of the reception signal is detected in such a way that the diffusion code is multiplied by the reception signal, before executing inverse-diffusion. Subsequently, such delay profile is integrated during fixed time by integrating-dump circuit. An amplitude square circuit executes amplitude square detection.
A control means shown in (d) selects three reception paths in the example of FIG. 1, in order of the largeness of the maximum value of the delay profile. The control means allocates the chip timing to respective tracking-fingers.
The tracking-finger shown in (c) executes inverse-diffusion of the reception signal using the diffusion code of each chip timing allocated previously to generate demodulating signal. The tracking-finger compares intensity of the reception signal which is subjected to inverse-diffusion using diffusion code whose chip phase is different by only xc2x1xcex94, namely, causing the chip timing to be moved before and after, thus tracking delay variation of the reception path using DLL (Delay Lock Loop).
Furthermore, the search-finger continues search of the reception path periodically shown in (d). The reception path which is tracked by the tracking-finger overlaps with each other. When the reception path with large reception signal intensity level occurs by another cause. In such the cases, re-allocation of the reception path to the tracking-finger is implemented.
In the first prior art, the demodulating signal outputted from respective tracking-fingers are obtained above such steps. Such the demodulating signal is detected to be demodulated with phase of pilot-symbol inserted in respective time slots of reception signal as a standard, thus the output signal is obtained by the fact that RAKE-composition is executed.
It requires very large calculation quantity to obtain the delay profile while executing correlating detection with accuracy of xc2xc to {fraction (1/16)} of the chip rate, for instance, in the above-described example, extending over wide search range such as extending over N symbols. For that reason, in the above-described first prior art, search of wide range according to the search-finger is restricted within fixed cycle. During this time interval, respective tracking-fingers monitor intensity level of the reception signal between two points with xc2x1xcex94, before executing tracking of the reception path.
Furthermore, the official report of the Japanese Patent Application Laid-Open No. HEI 10-32523 (hereinafter referred to as a second prior art) discloses the technique for obtaining the delay profile with required accuracy. According to the technique, the reception signal undergoes sampling with relatively rough sampling frequency, for instance, a sampling frequency of xc2xd of the chip rate. It calculates mutual correlation between the diffusion code and, for instance, the known signal list obtained from the pilot symbol. The obtained correlation value of two samples per one chip is interpolated by an interpolation filter so that the delay profile with required accuracy is obtained.
FIG. 2 is a block diagram showing a constitution of the searcher circuit of the second prior art. The searcher circuit of FIG. 2 comprises an A/D converter 101 for converting a complex base band signal obtained from radio band signal into a digital reception signal S, a list correlator 102 for obtaining mutual correlation between the digital reception signal S and well known signal list about fixed search range in every fixed cycle, an interpolation filter 103 for re-sampling an output signal R of the list correlator 102 with four times of sampling frequency of for instance, the A/D converter 101, a power calculator 104 for obtaining power P of the mutual correlation signal which is re-executed sampling in the interpolation filter 103, an averaging part 105 for obtaining the delay profile while adding to be averaged a mutual correlation signal power P extending over plural cycles, and a peak detector 106 for determining the most suitable reception timing xe2x80x9cxcfx84 optxe2x80x9d while obtaining peak xe2x80x9cPoptxe2x80x9d of the delay profile obtained by the averaging part 105.
The digital reception signal S is indicated as time list data of complex number with in-phase component of the complex base band signal as real number part, and with orthogonal component as imaginary number part, namely as time list data of vector value.
The list correlator 102 calculates the mutual correlation value while multiplying the time list data by complex conjugate.
For instance, the sampling frequency of the A/D converter 101 is taken as two times of the chip rate. As shown in FIG. 3, 1 time slot is constituted by transmission signal which consists of L symbols is diffused with a diffusion rate M (number of chip of diffusion code per 1 symbol) to be transmitted. On this occasion, signal component of symbol of m+1 th order in a slot of n+1 th order is diffused to the time list data from S (2LMn+2Mn+xcfx84) to S (2LMn+2Mn+2Mxe2x88x921+xcfx84) when xcfx84 is delay of reception path to the reception timing, namely known signal list Pn (i).
Consequently, from next formula, mutual correlation value Rnm (xcfx84) with respect to symbol concerned is obtained as a vector value.
Rnm(xcfx84)=xcexa3i=0 to Mxe2x88x921S(2LMn+aMn+xcfx84)xc3x97conj(Pn(j))
provided that conj ( ) represents complex conjugate.
Hereinafter, in the present specification, the mutual correlation value obtained by such procedure is represented as fading vector.
In the second prior art, the fading vector is obtained concerning required search range xcfx84=xcfx84min to xcfx84max. For instance the in-phase-addition (addition as vector value) is executed concerning the pilot symbol of Np symbol (N=Npxc3x97M chip) which is added to the front of respective slots. The profile in which reception timing xcfx84 of fading vector Rn (xcfx84) represented by formula below as time axis is taken as an output signal R of the list correlator 102 of the slot in order of m+1.
Rn(xcfx84)=xcexa3i=0 to Nxe2x88x921S(2LMn+2i+xcfx84)xc3x97conj(Pn(i))
The interpolation filter 103 obtains the profile with required delay precision by interpolating the profile of two times of the sample frequency of the chip rate obtained such procedure shown in FIG. 4.
In the example of FIG. 4, 0 vector is inserted in every xe2x85x9 chip as shown in (b) into the fading vector in every xc2xd chip of the profile (a) outputted by the list correlator 102. Thus, low pass filtering generates profile with accuracy of 8 times of the chip rate as shown in (c). The second prior art reduces required calculating quantity of the list correlator 102 to about xc2xc thereof according to the above procedure.
According to such procedure, the delay profile of the vector value which is in-phase added in every respective slots can be obtained.
However, the reception signal S is off concerning the phase between the slots. Therefore, it is incapable of improving S/N ratio (ratio of signal per noise) while executing the in-phase-addition, such that it is implemented to the adjacent pilot symbol.
For that reason, the interpolation filter 103 outputs chip rate. The delay profile has xe2x85x9 precision of such chip rate. The power calculator 104 obtains a power value (square sum of in-phase component and orthogonal component) of the fading vector of respective reception timing inserted of such delay profile. Subsequently, the power calculator 104 eliminates phase component. The averaging part 105 executes the power-addition, namely the averaging part 105 obtains mean value wile executing inter-slot addition of the power value of the same reception timing. The averaging part 105 outputs the delay profile which is power-added while averaging dispersion according to noise or change according to fading.
The peak detector 106 outputs one or plural reception timing xe2x80x9cxcfx84 optxe2x80x9d which give the maximum value of the power added delay profile under such procedure.
As described above, in the case where the delay profile for searching the reception path of the CDMA reception device is obtained, in the conventional method, the fading vector is in-phase added with respect to fixed time interval when it can be thought that the phase of the reception complex base band signal does not change in large scale, for instance concretely, in the above second prior art, the fading vector is in-phase-added concerning the pilot signal of Np symbol added to the front of respective slots. The prior art procedure obtains the delay profile of the vector value, before executing the power-addition extending over appropriate cycle to obtain required delay profile.
When change of transmission line of the reception path in between a plurality of delay profiles, namely radio band signal, is small, the suitable S/N ratio can be obtained using the in-phase-addition rather than the power-addition. However, in a practical manner, propagation characteristic of the transmission line changes from moment to moment.
When the phase of the reception complex base band signal is changed according to change of the propagation characteristic of the transmission line, the phase of the fading vector is changed according thereto. In such the case, if the in-phase-addition continues, it is incapable of obtaining effective delay profile, since the meaningful signal component is cancelled caused by the vector-addition.
Consequently, the conventional technique executes the in-phase-addition of the fading vector during fixed time interval uniformly to obtain the delay profile vector added, before power adding it to obtain the delay profile. Therefore, the conventional method has the problem that in the case where condition of the transmission line is changed largely as the mobile communication, it is not always obtained the effective delay profile.
In view of the foregoing, it is an object of the present invention, in order to overcome the above mentioned problem, to provide a reception path search method and a searcher circuit for use in such method of a CDMA reception device which monitors change of phase angle of fading vector to judge propriety of continuity of the in-phase-addition. The reception path search method and a searcher circuit for use in such method of the CDMA reception device controls number of the in-phase-addition appropriately to obtain effective delay profile whose S/N ratio is suitable.
According to a first aspect of the present invention, in order to achieve the above-mentioned object, there is provided a reception path search method of a reception device of CDMA (Code Division Multiple Access) communication system which comprises the steps of: generating a delay profile in every fixed cycle while executing plot of fading vector which is obtained in such a way that a reception signal converted into a complex base band signal is subjected to inverse-diffusion with known signal list in every reception timing about fixed range, generating an in-phase added delay profile while continuing vector-addition of the fading vector in every reception timing concerning continuous delay profile generated in every fixed cycle described above generating a power added delay profile while continuing the power-addition in every reception timing regarding fading vector with respect to continuous in-phase added delay profile, and searching an appropriate reception path while referring to the power added delay profile, wherein number of continuation of the vector-addition is taken to be variable, the reception path search method monitors a change of phase angle of the complex base band signal which change is reflected to respective delay profiles generated in every the fixed cycle, in the case where such phase angle is changed largely from settled angle of a threshold value, the reception path search method discontinues the continuation of the vector-addition, and then delay profiles which are in-phase added up to that time are taken as an object of the power-addition, before generating delay profile which is subjected to the power-addition.
According to a second aspect of the present invention, there is provided a reception path search method of a reception device of CDMA (Code Division Multiple Access) communication system which comprises the steps of: a delay profile generating step for generating a delay profile in every fixed cycle in such a way that the reception path search method causes fading vector to be plotted in every reception timing in connection with a fixed range, such fading vector is obtained in such a way that reception signal converted into complex base band signal undergoes inverse-diffusion using known signal list, a fading vector averaging step for calculating fading vector which is subjected to weighted-averaging such that the reception path search method selects maximum value of prescribed number more than one in order of the largeness from among the fading vector plotted in every reception timing in connection with respective these delay profiles, before executing weighted-averaging, a rotational comparison step for comparing an absolute value of an angle difference between a phase angle of the fading vector which is subjected to weighted-averaging and a phase angle of a basic vector maintained separately with an angle of a threshold value determined beforehand, before replacing the basic vector with the fading vector which is subjected to weighted-averaging when the absolute value of the angle difference is larger than the angle of threshold value, an in-phase-addition step for updating a delay profile which is subjected to the in-phase-addition in such away that when the absolute value of the angle difference is judged the angle difference is not larger than the angle of threshold value in such the rotational comparison step, the fading vector of the delay profile providing the fading vector which is subjected to weighted-averaging is executed a vector-addition in every reception timing to a fading vector of the delay profile which is subjected to the in-phase-addition maintained separately, while when the absolute value of the angle difference is judged the angle difference is larger than the angle of threshold value in such the rotational comparison step, the in-phase-addition step outputs the delay profile which is subjected to the in-phase-addition, as well as the in-phase-addition step updates the delay profile which is subjected to the in-phase-addition while replacing it with the delay profile providing the fading vector which is subjected to weighted-averaging, a power-addition step for calculating to be maintained delay profile which is subjected to the power-addition in such a way that the power-addition step executes cumulative addition of a power value of fading vector in every reception timing of the delay profile which is subjected to the in-phase-addition which is outputted in the in-phase-addition step, a delay profile outputting step for outputting delay profile which is subjected to the power-addition which is calculated to be maintained in the power-addition step whenever the number of times of generation of delay profile generated in every fixed cycle in the delay profile generating step comes to the number of times determined beforehand, and a reception path selecting step for selecting the most suitable reception timing of one or a plural number based on the delay profile outputted in the delay profile outputting step, before outputting as a reception path.
According to a third aspect of the present invention, in the second aspect, there is provided a reception path search method, wherein when the rotational comparison step judges that the absolute value of the angle difference is not larger than the angle of threshold value, the rotational comparison step does not execute updating of the basic vector.
According to a fourth aspect of the present invention, in the second aspect, there is provided a reception path search method, wherein when the rotational comparison step judges that the absolute value of the angle difference is not larger than the angle of threshold value, the rotational comparison step updates the basic vector, while executing vector-addition such that the rotational comparison step executes vector-addition between the fading vector which is subjected to weighted-averaging and the basic vector.
According to a fifth aspect of the present invention, in the second aspect, there is provided a reception path search method, wherein in the cases where the delay profile outputting step outputs the delay profile which is subjected to the power-addition, the delay profile which is subjected to the in-phase-addition in the in-phase-addition step is maintained on that occasion, in such the case, the delay profile outputting step executes the power-addition between the delay profile which is subjected to the in-phase-addition and the delay profile which is subjected to the power-addition, before outputting, and the delay profile outputting step clears the maintained delay profile which is subjected to the power-addition.
According to a sixth aspect of the present invention, in the second aspect, there is provided a reception path search method, wherein when the power-addition step executes cumulative addition in every reception timing in connection with power value of the fading vector in every reception timing of the delay profile which is subjected to the in-phase-addition in the in-phase-addition step, the power-addition step executes appropriate weighting cumulative addition in consideration of number of the in-phase-addition in the in-phase-addition step of the delay profile which is subjected to the in-phase-addition.
According to a seventh aspect of the present invention, there is provided a searcher circuit of CDMA (Code Division Multiple Access) communication system which comprises a delay profile generator for generating delay profile in every fixed cycle while plotting a fading vector which is obtained in such a way that a reception signal converted into a complex base band signal is subjected to inverse-diffusion using known signal list in every reception timing in relation to fixed range, a fading vector averaging part for calculating a fading vector which is subjected to weighted-averaging in such a way that the fading vector averaging part selects maximum number of prescribed number more than one in order of the largeness thereof from among the fading vector plotted in every reception timing in connection with respective delay profiles, a basic vector maintaining part for maintaining a basic vector, a rotational comparator for comparing an absolute value of an angle difference between a phase angle of the fading vector which is subjected to weighted-averaging and a phase angle of the basic vector with an angle of threshold value determined beforehand, and replacing the basic vector with the fading vector which is subjected to weighted-averaging when the absolute value of the angle difference is larger than the angle of threshold value, an in-phase adder for updating a delay profile which is subjected to the in-phase-addition in such a way that the in-phase adder executes vector-addition between a fading vector of the delay profile generated by the delay profile generator and a fading vector of a maintained delay profile which is subjected to the in-phase-addition in every reception timing, when such control is executed, the in-phase adder outputs the delay profile which is subjected to the in-phase-addition, and the in-phase adder replaces to be updated the delay profile which is subjected to the in-phase-addition by the delay profile generated by the delay profile generator, a power adder for calculating to be maintained a delay profile which is subjected to the power-addition in such a way that the power adder executes cumulative addition of power value of fading vector of every reception timing of the delay profile which is subjected to the in-phase-addition outputted from the in-phase adder in every reception timing, a controller for controlling the in-phase adder so as to output the delay profile which is subjected to the in-phase-addition, and so as to replace to be updated the delay profile which is subjected to the in-phase-addition by the delay profile generated by the delay profile generator when the controller judges that the absolute value of the angle difference between the phase angle of the fading vector which is subjected to weighted-averaging at the rotational comparator and phase angle of the basic vector is larger than the angle of threshold value, and for controlling the power adder so as to output a delay profile which is subjected to the power-addition which is calculated to be maintained in the power adder whenever the number of times of generation of a delay profile generated in every fixed cycle in the delay profile generator comes to the number of times determined beforehand.
According to an eighth aspect of the present invention, in the seventh aspect, there is provided a searcher circuit of CDMA (Code Division Multiple Access) communication system, wherein the rotational comparator does not update the basic vector when it is judged that the absolute value of the angle difference is not larger than the angle of threshold value.
According to a ninth aspect of the present invention, in the seventh aspect, there is provided a searcher circuit of CDMA (Code Division Multiple Access) communication system, wherein the rotational comparator updates the basic vector while executing vector-addition between the fading vector which is subjected to weighted-averaging and the basic vector when it is judged that the absolute value of the angle difference is not larger than the angle of threshold value.
According to a tenth aspect of the present invention, in the seventh aspect, there is provided a searcher circuit of CDMA (Code Division Multiple Access) communication system, wherein when the controller causes the power adder to be controlled so as to output the delay profile which is subjected to the power-addition, on this occasion, if the delay profile which is subjected to the in-phase-addition is maintained, the controller executes the power-addition between the delay profile which is subjected to the in-phase-addition and the delay profile which is subjected to the power-addition before outputting it and the controller controls the power adder so as to clear the maintained delay profile which is subjected to the power-addition.
According to an eleventh aspect of the present invention, in the seventh aspect, there is provided a searcher circuit of CDMA (Code Division Multiple Access) communication system, wherein when the power adder executes appropriate weighting cumulative addition in consideration of the number of times of the in-phase-addition in the in-phase adder of the delay profile which is subjected to the in-phase-addition, the power adder executes cumulative addition of power value of the fading vector of every reception timing of the delay profile which is subjected to the in-phase-addition outputted from the in-phase adder in every reception timing.